Red Shake King Block
From the Super Mario Wiki
The Red Shake King Block is a type of block that appears in the game Wario Land: Shake It! At first, these blocks will be fully visible. However, once Wario frees a Merfle from its cage, all the Red Shake King Blocks will turn transparent. Additionally, the Blue Shake King Blocks will turn solid during that incident, making them the exact opposite of each other.
Red Shake King Blocks tend to be placed in areas that Wario can't access right away. Most of the time, he has to free a Merfle in order to gain access to areas blocked by these blocks. The Red Shake King Blocks tend to keep Wario from making shortcuts to the Merfle cage, but once he frees the Merfle, Wario can use the shortcuts to get back to the level entrance and can also find treasures that have been previously blocked by the blocks.